1. Technical Field
The present invention generally relates to spark control for motor vehicle engines and, more particularly, to spark control for optimizing cold engine operation.
2. Discussion
It is known that high drivability index (DI) fuels have a slower burn rate when cold. It is also known that optimum torque points are different during cold engine operation than during warm engine operation due to the slower burn rate of high drivability index fuels. Therefore, without modification to the operating parameters of the engine, the potential for poor performance and fuel economy exists until the engine reaches a fully warm state.
One approach for compensating for the slower burn rate of high drivability index fuels during cold operation has been to enrich the fuel beyond stoichiometry. While this technique improves drivability, it has certain drawbacks. For instance, enriching the fuel may lead to poorer fuel economy than at stoichiometry. Further, enriching the fuel during cold operation may require frequent catalyst light off to burn excess fuel. This may lead to emission concerns as well as a possible reduction in the life of the catalyst.
In view of the foregoing, it would be desirable to compensate for the slower burn rate of high drivability index fuel during cold operation through the use of spark advance. It would also be desirable to use spark advance independently of or in concert with the fuel enrichment approach to account for lag during cold operation while protecting the catalyst and without sacrificing fuel economy.